Banca de QUALIFICAÇÃO: JOSE EWERTON DA SILVA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : JOSE EWERTON DA SILVA
DATE: 29/03/2022
LOCAL: sala virtual
TITLE:

AQUEOUS ELECTROSYNTHESIS OF CADMIUM CHALCOGENIDES TERNARY ALLOYS.

KEY WORDS:

Electrosynthesis; quantum dots; Cadmium Chalcogenides; ternary semiconductors.

PAGES: 70
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUMMARY:

The production of alloys of cadmium chalcogenides (CdSxSe1-x) is described in organic and aqueous colloidal synthesis methodologies, but it has never been electrochemically explored. Electrosynthesis provides an effective tool for the synthesis of Quantum Dots (QDs) presenting as main advantages the high reproducibility, reaction kinetic control and environmental appeal, by applying the electron as a reducing agent in the minimal presence of solvents. In this work, a simultaneous electroreduction process of multiple chalcogens was developed, where sulfur and selenium powder are reduced to form hydrogen sulfide (HS-) and selenide (Se2-) ions simultaneously and applied in the synthesis of CdSxSe1-x QDs. The molar ratio between HS- and Se2- ions was investigated (CdSxSe1-x, x = 0; 0,15; 0,35; 0,5; 0,65; 0,85, and 1) with the objective of modulating the optical parameters of the produced QDs. The nanoparticles were heat treated under reflux for two hours, at pH 9, for QDs growth. Through UV-Vis spectroscopy, it was possible to observe bands at 227 and 274 nm, characteristics of HS- and Se2- species. The synthesized QDs showed defined optical absorption bands, with bandgap between 2.42 and 2.84 eV for CdSe and CdS, respectively. The mixed chalcogenides present energies between CdSe and CdS with linear behavior of the bandgap with respect to the molar ratio, demonstrating controlled modulation of the optical parameters obtained. The XRD of the PQs suggests the presence of ternary alloys due to peak positions being between those of CdS and CdSe. The position of the energy bands was determined by cyclic voltammetry, where the HOMO and LUMO levels, as well as the band energy were determined as 2.79 and 3.06 eV for CdSe and CdS, respectively. The proof of concept that it is possible to reduce multiple chalcogenides to produce QDs was achieved, proving to be effective for synthesize  mixed cadmium chalcogenides. In this way, it is possible to expand to any chalcogenide-based systems, enabling  QD gap engineering for different applications.

BANKING MEMBERS:
Externo à Instituição - ANDERSON CAIRES DE JESUS - UFMG
Presidente - 2457389 - EDUARDO PADRON HERNANDEZ
Interna - 2163324 - JOANNA ELZBIETA KULESZA